Water-in-oil type emulsion ink for stencil printing

ABSTRACT

A water-in-oil type emulsion ink composed of 10-90% by weight of an oil phase and 90-10% by weight of an aqueous phase. The oil phase contains an esterified vegetable oil (an esterified vegetable oil obtained by recycling and esterifying edible waste oil such as soybean methyl ester, soybean butyl ester, or tall oil butyl ester).

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims under 35 USC 119, priority of JapaneseApplications No. 2003-25183 filed Jan. 31, 2003, 2003-142553 filed May20, 2003 and No. 2003-373671 filed Oct. 31, 2003, the disclosure ofwhich is hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

[0002] This invention relates to an emulsion ink of a water-in-oil (w/o)type useful for stencil printing and, more particularly, to awater-in-oil type emulsion ink for stencil printing which contains anesterified vegetable oil and which is environmentally friendly, safe andstable.

[0003] In stencil printing, an ink is applied onto a perforated stencilmaster backed by a printing paper and is passed through the perforationsto form an image on the printing paper. A well-known ink for use instencil printing is a water-in-oil type (w/o) emulsion ink containing avolatile solvent, a non-volatile solvent, a resin, a coloring agent, asurfactant, water, an antifreezing agent, an electrolyte and anantiseptic agent.

[0004] In recent years, an ink containing a vegetable oil is used as anink for stencil printing which is safe and stable in any environment andcan make good prints having a high image density and free from offset.

[0005] For example, JP-A-H10-245516 discloses a w/o type emulsion inkfor stencil printing containing an vegetable oil having an iodine valueof 100 or lower and a melting point of 0° C. or lower. In this ink, anon-volatile oil having an iodine value of 100 or lower is used toprevent solidification of the ink. However, water in the ink vaporizesand the viscosity of the ink decreases with time. As a result, an excessamount of the ink is loaded onto a paper to cause offset.

[0006] JP-A-H10-259341 discloses a w/o type emulsion ink for stencilprinting containing an animal fat or vegetable oil ester comprising afatty acid, and an oil or fat having a melting point of 20-55° C. Thus,when the ink is used after having been maintained in a low-temperatureenvironment, good prints cannot be made.

[0007] JP-A-2002-220560 discloses a w/o type emulsion ink for stencilprinting containing a vegetable oil having an iodine value of 110-150.This ink contains a vegetable oil having an iodine value of 110-150 andan oxidation inhibitor so that the ink does not cause clogging of thescreen or offset even when left unused for a long time. The oxidationinhibitor is dibutylhydroxytoluene, propyl gallate, butylhydroxyanisoleor the like. It is well known that these oxidation inhibitors are stablebut not safe. Thus, an oxidation inhibitor which is safer than theconventional oxidation inhibitors is demanded. However, under thecurrent circumstances, it is difficult to obtain an oxidation inhibitorexcellent in both stability and safety. In addition, when an oxidationinhibitor is used, the vegetable oil undergoes oxidation when the effectof the oxidation inhibitor is lost.

[0008] Oils used in making foods and beverages (waste edible oils) arerecycled and reused in the production of animal feed, soap and otherproducts or as fuel. However, waste edible oils are increasing everyyear and cannot be used up.

SUMMARY OF THE INVENTION

[0009] The present invention has been made to solve the above problemsand it is, therefore, an object of the present invention to provide aw/o emulsion ink for stencil printing which can make good prints andwhich is excellent in both stability and safety.

[0010] In accomplishing the foregoing objects, there is provided inaccordance with the present invention a w/o type emulsion ink forstencil printing comprising 10-90% by weight of an oil phase and 90-10%by weight of an aqueous phase, the oil phase containing an esterifiedvegetable oil.

[0011] The emulsion ink according to the present invention has excellentstability notwithstanding the fact that the ink contains a vegetable oilfor environmental friendliness. Since an esterified vegetable oil isless likely to be oxidized than a non-esterified vegetable oil, therecan be obtained a w/o type emulsion ink which is stable even when leftstand under service conditions on a printing machine and does not causeclogging. In addition, since there is no need to use an oxidationinhibitor, there can be obtained a safer w/o type emulsion ink.

[0012] Other objects, features and advantages of the present inventionwill become apparent from the detailed description of the preferredembodiments to follow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0013] The w/o type emulsion ink for stencil printing according to thepresent invention comprises 10-90% by weight of an oil phase and 90-10%by weight of an aqueous phase. The oil phase comprises an oil component(esterified vegetable oil) and, optionally, a pigment dispersing agent,a pigment, an extender, a resin, an emulsifier and other additives. Theaqueous phase comprises water and, optionally, an electrolyte, amildew-proof agent, water-evaporation preventive, a water-solublepolymer, an oil-in-water (o/w) type resin emulsion and other additives.As the above ingredients, known substances which do not adversely affectthe formation of an emulsion may be used without restriction.

[0014] Specific examples of the esterified vegetable oil include but arenot limited to esterified products of vegetable oils such as soybeanoil, tall oil, rapeseed oil, corn oil, rice oil, cotton oil, sesame oil,sunflower oil, safflower oil, olive oil, palm oil, coconut oil, linseedoil, palm kernel oil, and wood oil. Esterified products of vegetableoils recovered as waste edible oil after use and recycled can be alsoused. Examples of the edible waste oils include but not limited tovegetable oils recovered after being used to make tempuras or the likein restaurants and takeout food shops, or for school lunch. Any usedvegetable oil can be used as long as it is recyclable.

[0015] The vegetable oil is preferably esterified to a lower alkyl-ester(C1-C8 alkyl) such as a methyl ester, an ethyl ester, a butyl ester or acombination thereof.

[0016] The use of an esterified product of recycled waste edible oil ispreferred, since a w/o type emulsion ink for stencil printing which ismore environmentally friendly is obtainable. Conventionally, oils usedin making foods and beverages (waste edible oils) are recycled and usedin the production of animal feed, soap and other products or as fuel.However, waste edible oils are increasing every year and cannot be usedup. According to the present invention, waste edible oils can berecycled and used in the production of ink.

[0017] A methyl-esterified soybean oil is also preferable because it isless likely to be oxidized than refined soybean oil. Therefore, in thiscase, there can be obtained a w/o type emulsion ink for stencil printingwhich has high stability even when left stand under service conditionson a printing machine (which will be hereinafter referred to as servicestability). An ink containing at least 6% by weight of soybean oil basedon the weight of the ink is desirable since it meets the requirement fora soybean oil-based ink by the American Soybean Association.

[0018] A butyl-esterified soybean oil is less likely to be oxidized thanrefined soybean oil and is also preferable. By using thebutyl-esterified soybean oil, there can be obtained a w/o type emulsionink for stencil printing which has high service stability.

[0019] The use of a butyl-esterified tall oil, which is less likely tobe oxidized than tall oil, is also preferred, because there can beobtained a w/o type emulsion ink for stencil printing which has highservice stability. Since tall oil butyl ester has low volatility,components derived from vegetable oils can be increased in the ink.

[0020] The esterified vegetable oil for use in the present inventionpreferably has an ester value of 80-260, a melting point of lower than20° C. and an iodine value of about 130 or lower. When the melting pointis lower than 20° C., the ink can make good prints even when used afterbeing stored in a low temperature environment. When the iodine valueexceeds 130, the ink tends to dry quickly.

[0021] The content of the esterified vegetable oil in the ink ispreferably 5-20% by weight. As mentioned before, when the ink containsat least 6% by weight, based on the weight of the ink, of a vegetableoil derived from soybean oil, the ink meets the requirement for asoybean oil-based ink by the American Soybean Association.

[0022] If desired, the esterified vegetable oil may be used inconjunction with one or more other known oils such as a mineral oil, apetroleum solvent, a liquid paraffin and a spindle oil.

[0023] Illustrative of suitable paraffin oils are Gargoyle Arctic Oilseries (manufactured by Mobil Sekiyu Kabushiki Kaisha), Nisseki SuperOil series (manufactured by Nippon Oil Corporation), and Diana ProcessOil series and Diana Fresia series (manufactured by Idemitsu Kosan Co.,Ltd.).

[0024] As the mineral oil, a naphthene oil having a naphthenic carboncontent (C_(N)) of at least 30%, an aromatic carbon content (C_(A)) of20% or less and a paraffinic carbon content (C_(P)) of 55% or less asmeasured by ring analysis is suitably used. Illustrative of suitablenaphthene oils are Gargoyle Arctic Oil 155 and 300ID, Gargoyle ArcticOil Light and Gargoyle Arctic Oil C-Heavy (manufactured by Mobil SekiyuKabushiki Kaisha), Diana Process Oil series and Diana Fresia series(manufactured by Idemitsu Kosan Co., Ltd.), and Sunthene Oil series(manufactured by Japan Sun Oil Co., Ltd.).

[0025] Illustrative of petroleum solvents with high safety are ISOPARseries and EXXSOL series (manufactured by Exxon Chemicals Co., Ltd.),and AF Solvent series (manufactured by Nippon Oil Co., Ltd.).

[0026] Further, for reasons of stability, the oil component preferablyhas less than 3% by weight of a content of polycyclic aromatic compoundsincluding aromatic compounds having at least three condensed aromaticrings.

[0027] In addition, an aroma oil with high safety may be used whennecessary. The aroma oil may be as disclosed in JP-A-H11-80640 and havea mutagenicity index (MI) of less than 1.0, an aromatic carbon content(%C_(A)) of 20-55%, an aniline point of not higher than 100° C., a totalpolycyclic aromatics content of not greater than 50 ppm by weight basedon a total oil content of the oil and a content of individual polycyclicaromatic of not greater than 10 ppm by weight. The polycyclic aromaticsmay include benzo[a]anthracene, benzo[b]fluoranthene,benzo[j]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene anddibenzo[a, j]acridine.

[0028] These oils may be used singly or in combination of two or morethereof.

[0029] The coloring agent for use in the present invention may be anyknown pigment or dispersing dye. An insoluble pigment or dye ispreferably used. Examples of the coloring agents include carbon blacksuch as acetylene black, channel black and furnace black; metal powdersuch as aluminum powder and bronze powder; inorganic pigments such asred oxide of iron, chrome yellow, ultramarine blue, chromium oxide andtitanium oxide; azo pigments such as insoluble azo pigments, azo lakepigments and condensed azo pigments; phthalocyanin pigments such asmetal-free phthalocyanin pigments and a copper phthalocyanin pigment;condensed polycyclic pigments such as anthraquinone pigments,quinacridone pigments, isoindolinone pigments, isoindolin pigments,dioxazine pigments, threne pigments, perylene pigments, perinonepigments, thioindigo pigments, quinophthalone pigments and metal complexpigments; organic pigments such as lake of acid or basic dyes; diazodyes; anthraquinone dyes; carbonyl dyes; quinonimine dyes; methine dyes;quinoline dyes; nitro dyes; and fluorescent pigments. These pigments anddyes may be used singly or in combination of two or more thereof.

[0030] The fluorescent pigment suitably used for the purpose of thepresent invention is in the form of a synthetic resin matrixcomposited-type in which a fluorescent dye is supported by the resinmatrix. The composite is prepared by dissolving the dye in apolymerization reaction solution or product, and then finely pulverizingthe dye-bearing polymer. The polymer may be, for example, a melamineresin, a urea resin, a sulfonamide resin, an alkyd resin or a polyvinylchloride resin.

[0031] When carbon black is used as the pigment, acidic carbon blackhaving a pH of less than 5 is preferably used for incorporation into theoil phase. Examples of suitable carbon black pigments include CarbonBlack MA-100, MA-7, MA-77, MA-11, #40 and #44 (products of MitsubishiChemical Corporation) and Raven 1100, Raven 1080, Raven 1255, Raven 760,and Raven 410 (products of Columbian Carbon Japan Ltd.).

[0032] The coloring agent is incorporated into at least one of the oilphase and the aqueous phase. Thus, the above exemplified coloring agentsmay be also used for the incorporation into the aqueous phase. Thepigment to be dispersed in the oil phase and/or aqueous phase preferablyhas an average particle size of 0.1-10 μm, more preferably 0.1-1 μm. Theamount of the pigment is suitably determined according to the intendedcolor density of the prints and is generally in an amount of 2-15% byweight based on the ink. Two or more coloring agents of similar typesmay be incorporated into the same phase. Two coloring agents ofdifferent colors may be incorporated into the same phase or differentphases. When pigments of different types (color tone, specific gravity,etc.) are used, the pigments are preferably incorporated into differentphases to avoid problems which may occur when the pigments contact witheach other.

[0033] When a coloring agent is incorporated into the oil phase inaddition to the aqueous phase, the uniformity of printed images can beimproved. When an ink penetrates into paper, the oil componentsurrounding the aqueous phase penetrates into the paper first and thenthe aqueous phase penetrates into the paper. When the fibers of thepaper are wet with oil, the wettability of the fibers of the paper withthe water phase decreases and the aqueous phase component cannot spreadin the paper. When a coloring agent is incorporated into the oil phaseas well as into the aqueous phase, the coloring agent can adheres to thefibers of the paper uniformly and image uniformity can be improved. Whena coloring agent is incorporated only into the oil phase, the aqueousphase component attached to the fibers of the paper rejects the oilphase component and prevents the coloring agent from adhering properly.Thus, sufficient image uniformity cannot be obtained.

[0034] An emulsifier is used for the formation of a water-in-oil typeemulsion. The emulsifier is preferably a nonionic surfactant such as afatty acid ester of sorbitan, a fatty acid ester ofpolyoxyethylene-sorbitan, (poly)glyceride of a fatty acid, apolyoxyethylenesorbitol fatty acid ester, a polyoxyethyleneglycerolfatty acid ester, a polyethylene glycol fatty acid ester,polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether,polyoxyethylenealkylamine, a fatty acid amide, polyoxyethylenepolyoxypropylene alkyl ether, polyoxyethylene castor oil, hardenedcastor oil, and higher alcohols. These surfactants may be used singly orin combination of two or more thereof. Two or more emulsifiers withdifferent HLB may be used in combination to prepare an emulsion withhigh stability. The emulsifier is used in an amount of 1-8% by weight,preferably 2-5.5% by weight, based on the weight of the ink.

[0035] A resin is incorporated into the oil phase to keep the pigment insuspension. Illustrative of suitable resins are rosin; rosin derivativessuch as polymerized rosin, hydrogenated rosin, esterified rosin, rosinpolyester resins, hydrogenated and esterified rosin; rosin-modifiedresins such as rosin-modified alkyd resins, rosin-modified maleic acidresins and rosin-modified phenol resins; maleic acid resins; phenolresins; petroleum resins; rubber-derived resins such as cyclizedrubbers; terpene resins; alkyd resins; and polymerized castor oil. Theseresins may be used singly or as a mixture of two or more thereof. Aboveall, the use of alkyd resins is preferred in particular. The resinincorporated into the oil phase improves the adhesion of the ink to thepaper.

[0036] An alkyd resin is constituted from a fat or oil, a polybasicacid, and a polyhydric alcohol. Examples of fats and oils includenon-drying oil and semi-drying oil having an iodine value of 80 or lessand fatty acids of these oils, such as coconut oil, palm oil, olive oil,castor oil, rice bran oil and cotton oil. Drying oil such as soybeanoil, linseed oil and tung oil may also be used as long as the resultingalkyd resin has an iodine value of 80 or less.

[0037] Examples of the polybasic acids include saturated polybasic acidssuch as phthalic anhydride, isophthalic acid, terephthalic acid,succinic acid, adipic acid, sebacic acid, tetrahydrophthalic acid; andunsaturated polybasic acids such as maleic acid, maleic anhydride,fumaric acid, itaconic acid and citraconic anhydride.

[0038] Examples of polyhydric alcohols include ethylene glycol,diethylene glycol, triethylene glycol, polethylene glycol, propyleneglycol, trimethylene glycol, tetramethylene glycol, glycerin,trimethylolpropane, neopentyl glycol, diglycerin, triglycerin,penthaerythritol, dipentaerythritol, mannitol and sorbitol.

[0039] The alkyd resin preferably has an oil length of 60-90 and aniodine value of 80 or less for reasons of dispersion stability andprevention of clogging of the cylinder screen caused by film formation.The term “oil length” of the alkyd resin used herein is intended torefer to a percentage of the weight of the fatty acids contained in thefat and oil based on the weight of the alkyd resin when calculated interms of triglycerides. The alkyd resin preferably has a molecularweight of less than 30,000, more preferably 10,000 or less.

[0040] The resin to be incorporated into the oil phase is preferablyused in an amount of 2-50% by weight, more preferably 5-20% by weight,based on the weight of the oil phase, for reasons of cost and printingproperty of the ink.

[0041] The resin preferably has a weight average molecular weight of8,000-160,000, more preferably 30,000-80,000, for reasons of printingproperty of the ink. Too large an amount of the resin and too high amolecular weight of the resin would cause a problem of ink leakage,while a too small an amount and a too low a molecular weight of theresin would cause a problem in fixation of the ink.

[0042] Examples of the resins are KG-836, KG-846, KG-1801, KG-1832,KG-1829, KG-1804, KG-1828, KG-1808-1, KG-1834, KG-1831, KG-1833, TAMANOL353, TAMANOL 403, TAMANOL 371, TAMANOL 394 (products of Arakawa ChemicalIndustries Ltd.), HARIPHENOL 561, 564, 582, 173, T-3120, T-3040, P-637,and 295 (products of Harima Chemicals Inc.).

[0043] As the dispersing agent for the coloring agent for use in the oilphase, a dispersing agent which does not adversely affect the formationof the emulsion is used. The nonionic surfactants and water-solublepolymers for the emulsifier may be used. Other examples are alkylamineshaving a high molecular weight, aluminum chelate compounds,styrene-maleic anhydride copolymers, high molecular weightpolycarboxylic acid esters, aliphatic polycarboxylic acids, amine saltsof polyesters, ester-type anionic surfactants, long chain amine salts ofhigh molecular weight polycarboxylic acids, salts of long chainpolyaminoamides with polyesters, polyamides, phosphoric acid estersurfactants, salts of alkylsulfocarboxylic acids, salts ofα-olefinsulfonic acids, salts of dioctylsulfosuccinic acid, polyethyleneimines, salts of alkylolamines and resins capable of dispersing theinsoluble coloring agents such as alkyd resins. An anionic, cationic oramphoteric surfactant may also be used as the dispersing agent as longas it does not adversely affect the storage stability of the ink.

[0044] The above-described dispersing agents may be used singly or as amixture of two or more. The dispersing agent which is a resin or apolymer is used in an amount of 40% by weight or less, preferably 2-35%by weight, based on the weight of the pigment. The dispersing agentwhich is not a resin or a polymer is used in an amount of 40% by weightor less, preferably 2-35% by weight, based on the weight of the pigment.

[0045] Alkyd resins improve the dispersion stability of the insolublecoloring agent when a resin with a high molecular weight is added. Whenan alkyd resin is used singly or in combination of other dispersingagents, the alkyd resin is preferably used in an amount of at least 0.05parts by weight per part by weight of the pigment.

[0046] A gelation agent serves to form a gel of the resin contained inthe oil phase and to improve the storage stability, fixation propertyand fluidity of the ink. Thus, it is preferred that the gelation agentbe capable of forming a coordinate bond with the resin contained in theoil phase.

[0047] Illustrative of suitable gelation agents are organic acid salts,organic chelates and metal soap oligomers containing Li, Na, K, Al, Ca,Co, Fe, Mn, Mg, Pb, Zn or Zr. Specific examples of the gelation agentinclude metal salts of octylic acid such as aluminum octylate, metalsalts of naphthenic acid such as manganese naphthenate, metal salts ofstearic acid such as zinc stearate, and organic chelates such asaluminum diisopropoxide monoethylacetoacetate. These gelation agents maybe used singly or as a mixture of two or more thereof and is generallyused in an amount of not more than 15% by weight, preferably 5-10% byweight, based on the weight of the resin component in the oil phase.

[0048] Although the emulsion ink for stencil printing according to thepresent invention is stable without an oxidation inhibitor, an oxidationinhibitor may be used to improve the stability, if desired. Theoxidation inhibitor to be incorporated into the oil phase may be, forexample, dibutylhydroxytoluene, propyl gallate and butylhydroxyanisoleand is generally used in an amount of 2% by weight or less, preferably0.1-1% by weight, based on the weight of the oil component in the ink.If desired, two or more oxidation inhibitors may be used in combination.

[0049] An extender may be added in the ink to control the viscosity ofthe ink and to prevent ink blurs.

[0050] The extender may be incorporated into the oil phase and/oraqueous phase. The extender may be fine particles of inorganic materialssuch as clay, silica, talc, calcium carbonate, barium sulfate, titaniumoxide, alumina white, diatomaceous earth, kaolin, mica and aluminumhydroxide, or fine particles of organic materials such as polyacrylicester, polyurethane, polyester, polyethylene, polypropylene, polyvinylchloride, polyvinylidene chloride, polystyrene, polysiloxane, phenolresins, epoxy resins and copolymers thereof.

[0051] The extender is used in an amount of 0.1-50% by weight,preferably 1-5% by weight, based on the ink.

[0052] The electrolyte in the aqueous phase serves as an emulsionstabilizer. Thus, an electrolyte is used when the aqueous phase does notcontain any material which is adversely affected by the electrolyte.

[0053] A salt providing anions such as citrate ions, tartrate ions,sulfate ions and acetate ions, or a salt providing cations such asalkali metal ion and alkaline earth metal ions may be suitably used.Illustrative of suitable electrolytes are magnesium sulfate, sodiumsulfate, sodium citrate, sodium hydrogenphosphate, sodium borate, andsodium acetate. These electrolytes may be used singly or in combinationof two or more thereof. The electrolyte is generally used in an amountof 0.1-2% by weight, preferably 0.5-1.5% by weight, based on the weightof the aqueous phase.

[0054] A water-soluble polymer and/or an oil-in-water (o/w) typeemulsion may be incorporated into the aqueous phase of the emulsion inkas a viscosity controlling agent, a wetting agent for the prevention ofdrying of the aqueous phase, and to improve the dispersion and adhesionof the insoluble coloring agent and the extender.

[0055] As the water-soluble polymer, both natural and synthetic polymersmay be used. Examples of water-soluble polymers include natural polymerssuch as starch, mannan, sodium alginate, galactan, tragacanth rubber,gum Arabic, pullulan, dextran, xanthan rubber, glue, gelatin, collagen,and casein; semi-synthetic polymers such as carboxymethyl cellulose,hydroxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose,hydroxypropyl cellulose, hydroxypropyl methylcellulose, hydroxymethylstarch, carboxymethyl starch, dialdehyde-type starch; neutralizationproducts such as acrylic resins and sodium salt of polyacrylic acid;polyvinylimide; polyvinyl alcohol; polyvinyl pyrrolidone;polyethylenimine; polyacrylamide; poly-N-alkylsubstituted acrylamidesuch as poly-N-acryloylpyrrolidine and poly-N-isopropylacrylamide;polyethylene oxide; polyvinyl methyl ether; styrene-maleic anhydridecopolymer; styrene-acrylic acid copolymer and a polymer obtained byincorporating alkyl groups into the above copolymer for impartinghydrophobicity. Acrylamide polymers and acrylic polymers may be of apartly hydrophobic copolymer-type in which alkyl groups are incorporatedinto part of the monomer units. A block-copolymer of polyethylene andpolypropylene or polybutylene may also be used.

[0056] The above water-soluble polymers may be used singly or incombination with two or more thereof. The amount of the water-solublepolymer is generally 25% by weight or less, preferably 0.5-15% byweight, based on the weight of the water contained in the ink.

[0057] The o/w type emulsion contains a synthetic or natural polymer.The synthetic polymer may be, for example, polyvinyl acetate, acrylicester, methacrylic ester, vinyl chloride, ethylene-vinyl acetatecopolymer, vinyl acetate-acrylic ester copolymer, styrene-acrylic estercopolymer, vinylidene chloride-acrylic ester copolymer, vinylchloride-vinyl acetate copolymer, or urethane. The natural polymer asused in the oil phase may be used for the formation of the o/w typeemulsion.

[0058] Two or more different kinds of o/w type emulsions may be used aslong as they do not affect the stability of the w/o type emulsion ink.The emulsion may be prepared in any known emulsifying method using asuitable dispersing agent, a protective colloid or a surfactant.Soap-free emulsion polymerization may also produce the o/w typeemulsion. It is preferred that the o/w emulsion have a minimum filmforming temperature of not higher than 40° C.

[0059] The mildew-proof agent is used for the prevention of growth ofmolds or germs in the ink during storage. It is recommendable to use amildew-proof agent when the emulsion ink of the present invention isintended to be stored for a long period of time. Illustrative ofsuitable mildew-proof/antiseptic agent are aromatic hydroxyl compoundsor their chlorinated derivatives such as salicylic acid, phenolcompounds, methyl p-oxybenzoate and ethyl p-oxybenzoate; sorbic acid anddehydroacetic acid. These compounds may be used singly or in combinationof two or more thereof. The mildew-proof agent is generally used in anamount of not greater than 3% by weight, preferably 0.1-1.2% by weight,based on the weight of the water in the ink.

[0060] The antifreezing agent which may also serve as a wetting agentmay be, for example, glycols such as ethylene glycol, diethylene glycoland propylene glycol; lower saturated monohydric alcohols such asmethanol, ethanol, isopropanol, butanol and isobutanol; and polyhydricalcohols such as glycerin and sorbitol.

[0061] These compounds may be used singly or in combination of two ormore thereof. The amount of the antifreezing agent is generally notgreater than 15% by weight, preferably 4-12% by weight, based on theweight of the water in the ink.

[0062] If desired, a pH controlling agent, such as triethanolamine,sodium acetate, triamylamine, sodium hydroxide, or ammonia, is used tomaintain the pH of the aqueous phase at a suitable range of 6-8. ThepH-controlling agent can serve to increase the viscosity of the ink byincorporation of the water-soluble polymer. Too high or low pH adverselyaffects the effect of the water-soluble polymer as a viscositycontrolling agent.

[0063] If desired, a wax may be incorporated into the oil phase for thepurpose of improving separation between a printing drum and printingpaper or of preventing the sticking of printing paper. The aqueous phasemay contain triethanolamine or sodium hydroxide, which can serve toincrease the viscosity of the ink by incorporation of the water-solublepolymer. If desired, other conventional additives such as a preservativefor the prevention of rust of a printer and an anti-foaming agent may beincorporated into the aqueous phase in a suitable amount.

[0064] The w/o type emulsion ink according to the present invention maybe prepared by any known method. For example, an oil phase in the formof an aqueous dispersion containing, for example, a pigment, anemulsifier, a resin and other additives is prepared at room temperature.An aqueous phase containing a mildew-proof/antiseptic agent, awater-soluble polymer, and other additives is then gradually mixed withthe oil phase to form an emulsion.

[0065] The viscosity of the ink may be adjusted also by stirringconditions for the formation of the emulsion. It is desirable to adjustthe viscosity of the ink to. 3-40 Pa·s, more preferably 6-30 Pa·s, at ashear rate of 20 s^(−1,) though any viscosity may be adopted as long asthe ink can meet with a given printing system.

[0066] The following examples will further illustrate the presentinvention.

EXAMPLES 1-9 Comparative Example 1

[0067] A coloring agent, oil(s) and a dispersing agent as shown belowwere mixed and kneaded with three rolls. The resulting dispersion wasmixed with a vanish containing an emulsifier and oil(s) as shown belowto obtain an oil phase. An aqueous phase containing water, ananti-freezing agent, an electrolyte and a mildew-proof agent as shownbelow was gradually added to the oil phase using an emulsifying deviceto obtain a w/o type emulsion ink having the composition shown below.

[0068] In Examples 1-9 and Comparative Example 1, the carbon black isMA-77 (product of Mitsubishi Chemical Corporation), and the pigmentdispersant (aluminum chelate) is Plenact AL-M (product of AjinomotoInc.). The mineral oils are paraffin oils manufactured by Mobil SekiyuKabushiki Kaisha (Gargoyle Arctic Oil Light and Gargoyle Arctic Oil). Asthe phthalocyanine blue, vegetable oils (soybean oil, ester value: 190,iodine value: 132, soybean oil methyl ester, ester value: 195, iodinevalue: 120, evaporation rate: 4.80%, soybean oil butyl ester, estervalue: 170, iodine value: 100, evaporation rate: 0.93%, tall oil butylester, iodine value: 110, acid value: 2, evaporation rate: 0.067%,castor oil, iodine value: 86, freezing point: −14° C.), sorbitansesquioleate, ion-exchanged water, ethylene glycol, magnesium sulfate,and methyl p-oxybenzoate, commercially available products were used. Theevaporation rates were measured according to ASTM D6419. TABLE 1 Unit:parts by weight Example 1 2 3 4 Comparative example 1 Pigment Carbonblack 4.5 4.5 4.5 4.5 4.5 Phthalocyanin 0.5 0.5 0.5 0.5 0.5 BlueDispersing Aluminum chelate 0.5 0.5 0.5 0.5 0.5 agent for PigmentMineral oil Gargoyle Arctic 10.7 oil light Gargoyle Arctic 10.7 10.710.7 oil 1046 Vegetable Soybean oil 10.0 oil methyl ester Soybean oil10.0 butyl ester Soybean oil 8.0 18.7 isobutyl ester Tall oil butylester Castor oil Soybean oil 10.0 2.0 2.0 Oxidation Butyl- inhibitorhydroxyanisole Emulsifier Sorbitan 4.0 4.0 4.0 4.0 4.0 sesquioleateWater Ion-exchanged 58.7 58.7 58.7 58.7 58.7 water Anti- Ethylene glycol10.0 10.0 10.0 10.0 10.0 freezing agent Electrolyte Magnesium 1.0 1.01.0 1.0 1.0 sulfate Mildew- Methyl 0.1 0.1 0.1 0.1 0.1 proof agentp-oxybenzoate

[0069] TABLE 2 Unit: parts by weight Example 5 6 7 8 9 Pigment Carbonblack 4.5 4.5 4.5 4.5 4.5 Phthalocyanin 0.5 0.5 0.5 0.5 0.5 BlueDispersing Aluminum chelate 0.5 0.5 0.5 0.5 0.5 agent for PigmentMineral oil Gargoyle Arctic 10.7 oil light Gargoyle Arctic 10.7 9.7 oil1046 Vegetable Soybean oil 6.0 16.0 7.0 10.0 oil methyl ester Soybeanoil 7.0 isobutyl ester Tall oil butyl 10.0 6.7 ester Castor oil 4.0 4.7Soybean oil Oxidation Butyl- 1.0 inhibitor hydroxyanisole EmulsifierSorbitan 4.0 4.0 4.0 4.0 4.0 sesquioleate Water Ion-exchanged 58.7 58.758.7 58.7 58.7 water Anti- Ethylene glycol 10.0 10.0 10.0 10.0 10.0freezing agent Electrolyte Magnesium 1.0 1.0 1.0 1.0 1.0 sulfate Mildew-Methyl 0.1 0.1 0.1 0.1 0.1 proof agent p-oxybenzoate

[0070] Each of the emulsion inks was tested for stability when leftstand under service conditions on a printing machine. The results aresummarized in Table 3. As is clear from the results, the emulsion inkaccording to the present invention is not solidified and does not causeclogging of the screen even after having been left on a stencil printingmachine for a long time. Since the oils used in examples 4, 6 and 8 areall vegetable oils, the emulsion inks of Examples 4, 6 and 8 areenvironmentally friendly. Especially, since the oils used in Example 8are all recycled vegetable oils, the emulsion ink of Example 8 is moreenvironmentally friendly.

[0071] Service Stability:

[0072] To evaluate the service stability of the emulsion ink, thefollowing two tests were conducted.

[0073] (1) The drum of a printing machine has been left in an oven at60° C. for one week. Then, printing is again conducted and the printsare observed with naked eyes to evaluate the time it took to get a goodprint.

[0074] A: a complete image can be printed in a short period of time

[0075] B: it takes some time until a complete image can be printed

[0076] C: it takes long time until a complete image can be printed (or acomplete image cannot be printed)

[0077] (2) Ink sample put in a petri dish is left in open air at 60° C.for one week. The difference in viscosity before and after being left isevaluated on the basis of the following ratings:

[0078] A: not increased

[0079] B: slightly increased

[0080] C: significantly increased TABLE 3 Example 1 2 3 4 5 6 7 8 9Comparative example 1 (1) A A C A A A A A A A (2) A A C A A A A A A A

EXAMPLES 10-13 Comparative Examples 2

[0081] A mixture of a coloring agent, a dispersing agent for thecoloring agent, and water as shown in Table 4 was passed through a beadsmill. The resulting dispersion was mixed with an antifreezing agent, anantiseptic agent and a water-soluble resin as shown in Table 4 to obtaina coloring agent-containing aqueous phase. Oils, an emulsifier andoptionally a resin as shown in Table 5 were mixed to obtain an oilphase. The aqueous phase was gradually added to the oil phase using anemulsifying device to obtain a w/o type emulsion ink.

EXAMPLE 14

[0082] A coloring agent, oil(s) and a dispersing agent as shown in Table5 were mixed and kneaded with three rolls. The resulting dispersion wasmixed with a vanish containing an emulsifier, a resin and oil(s) asshown below to obtain an oil phase. The aqueous phase was graduallyadded to the oil phase using an emulsifying device to obtain a w/o typeemulsion ink. TABLE 4 Unit: parts by weight Example 10 11 12 13 14Comparative example 2 Coloring Carbon 6.0 6.0 6.0 6.0 4.0 6.0 agentblack Extender Talc 0.1 Pigment Water- polyvinyl 2.0 2.0 2.0 2.0 1.5 2.0soluble pyrrolidone polymer (K-30) Dispersing Sulfonic 0.5 0.5 0.5 0.50.3 0.5 agent for acid coloring surfactant agent Water Ion- 57.4 57.451.4 51.4 56.9 57.4 exchanged water Anti- Ethylene 10.0 10.0 10.0 10.010.0 10.0 freezing glycol agent Anticeptic Methyl p- 0.1 0.1 0.1 0.1 0.10.1 agent oxybenzoate

[0083] TABLE 5 Unit: parts by weight Example 10 11 12 13 14 Comparativeexample 2 Coloring Carbon 2.0 agent black Phthalo- 0.1 cyanin BlueDispersing Aluminum 0.5 agent for chelate coloring agent ExtenderTitanium 0.1 oxide Resin Haliphenol 3.0 1.0 173 Mw: 60,000 MineralGargoyle 3.0 9.5 10.0 oil Arctic oil light Gargoyle 10.0 Arctic oil 1046Vegetable Soybean oil 10.0 10.0 12.07 10.0 oil methyl ester Soybean oil20.0 6.0 isobutyl ester Tall oil 10.0 8.0 butyl ester Soybean oil 10.0Emulsifier Sorbitan 4.0 4.0 4.0 4.0 4.0 4.0 monoioleate

[0084] Each of above w/o type emulsion inks was tested for servicestability, fixation and uniformity of a solid pattern according to thefollowing methods. The results are summarized in Table 6.

[0085] Service Stability:

[0086] Evaluation is made in the same manner as in examples 1 to 9.

[0087] Fixation:

[0088] A sample image is printed in a paper using a commerciallyavailable printing machine, (Satelio A400 manufactured by Ricoh Company,Ltd.). The image is rubbed with fingers and the fixation of the ink isobserved with naked eyes. The evaluation is rated as follows:

[0089] A: excellent

[0090] B: good

[0091] C: not good

[0092] Uniformity of Solid Pattern:

[0093] A solid pattern is printed on a paper using a commerciallyavailable printing machine, (Satelio A400 manufactured by Ricoh Company,Ltd.). The image is observed with naked eyes and a magnifier. Evaluationof uniformity of solid pattern is rated as follows:

[0094] A: no small void is observed

[0095] B: image is uniform but small voids are observed

[0096] C: image is not uniform and many small voids are observed TABLE 6Example 10 11 12 13 14 Comparative Example 2 Service B B B B B Cstability (1) Service B B B B B C stability (2) Fixation B B B A A AUniformity of B B B B A B solid pattern

[0097] The invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Thepresent embodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all the changes which come within the meaning and rangeof equivalency of the claims are therefore intended to be embracedtherein.

What is claimed is:
 1. A water-in-oil type emulsion ink comprising10-90% by weight of an oil phase and 90-10% by weight of an aqueousphase, said oil phase containing an esterified vegetable oil.
 2. Awater-in-oil type emulsion ink as claimed in claim 1, wherein saidesterified vegetable oil is obtained by recycling and esterifying anedible waste oil.
 3. A water-in-oil type emulsion ink as claimed inclaim 1 or 2, wherein said esterified vegetable oil contains soybean oilmethyl ester.
 4. A water-in-oil type emulsion ink as claimed in claim 1or 2, wherein said esterified vegetable oil contains soybean oil butylester.
 5. A water-in-oil type emulsion ink as claimed in claim 1 or 2,wherein said esterified vegetable oil contains tall oil butyl ester. 6.A water-in-oil type emulsion ink as claimed in any one of claims 1 to 5,wherein said aqueous phase contains a coloring agent.
 7. A water-in-oiltype emulsion ink as claimed in any one of claims 1 to 6, wherein saidoil phase contains a resin.
 8. A water-in-oil type emulsion ink asclaimed in any one of claims 1 to 7, wherein said oil phase contains acoloring agent.